Can anyone tell me if a hand vacuum pump will get enough of a vacuum
in a bell jar to debubble resins and epoxy? The epoxy I’m using has a
very thin consistency, about like olive oil. I hate to spend the
$300 on a vacuum compressor if I can get away with a $50 hand pumped
model.

If anyone else has a good way of doing this on the cheap, I’d love
to hear about it.

I have been using Colores ™ brand and with the thin hardener I
have been happily surprised that the formula has a tendency to
eliminate air bubbles as it cures. Of course the cure time is several
hours and that may be part of it. Carbon dioxide blown over the top
of the epoxy resin before and as it cures also eliminates air bubbles
without vacuuming.

Depending on the cure time or pot life of the epoxy resin you are
using there may not be enough time to vacuum out the bubbles with a
hand pumped vacuum. I would suggest using an extended cure time resin
and then the 15 to 25 minutes of pumping with a hand pump to get a
vacuum won’t be wasted.

Don, there are two factors to consider. First the viscosity of the
resin, which is probably published on the label. Second, it is a good
idea to think in terms of a vacuum pump capable of 27 inches Hg and
more. I don’t know what can be achieved with a hand pump.

Here is some of what we have learned in making and selling high
strength Silicone RTV mold rubbers. Many, many jewelers do not have
vacuum pumps that dependably achieve 29 inches Hg. There are many
reasons, not limited to improper care and maintenance and home built
systems that have not been well constructed. They just don’t pull
enough vacuum for the typical high viscosity of most high strength
silicone RTVs, which tend to have viscosity levels as high as 1000
poise.

We recently introduced our LOVIS silicone RTVs, which have viscosity
of only 200 poise. The folks who did not have success with silicones
are now de-airing comfortably at 27 inches.

If the resins you wish to de-air are 200 poise and lower, you will
be OK at around 27 inches, but you will have to find out what the
hand pump is capable of doing first.

Finally, I can’t think of any situation where it is good practice to
do your work in a half-butted manner. Go for the dependable vacuum
pump and forget the hand job. You will have far wider capabilities
and less to worry about.

Instead of a vacuum, would pressure do the trick? A process I
learned from some pen turners is to use a paint pressure pot to
de-bubble cast resin pen blanks. They mix up resin, add pigment and
put into a 2"x3"x1" mold and then put that into a paint pressure pot.
Still some speculation on what optimal pressure is, but seems they
are getting pretty consistent results between 30-45psi. Let sit for a
couple of hours or how ever long it takes for the resin to start to
solidify. I don’t really know that it needs to really set any longer
than it takes for the resin to set. Anyway after the process the
result is a cast block that is bubble free.

You won’t be able to see the piece in the pot and the set time of
the resin would obviously be critical.

What about a Venturi - I think that’s what they’re called. Available
from scientific supply companies.

It’s a metal, sort of funnel shaped piece that creates a vacuum using
running water. The top (wide end) of the funnel attaches to your water
supply and runs out a thin tube at the bottom.

There is another metal tube coming out the side that your vacuum hose
would attach to. The water running through the funnel pulls the air
from the tube along with it and that creates the vacuum. I’ve seen it
used for debubbling investment. Of course you need a decent supply of
running water in your shop but beyond that it’s quite low tech and
effective.

What about a Venturi - I think that's what they're called.
Available from scientific supply companies.

It’s a metal, sort of funnel shaped piece that creates a vacuum
using running water. The top (wide end) of the funnel attaches to
your water supply and runs out a thin tube at the bottom.

I know it as an aspirator. Have one, used one, it works, at sea
level, not here in Denver. Top attaches like you say, water runs
thru, piece of metal that has a twist produces the vacuum, and a
hose connects to the side where the vacuum is produced.

You can also get a used air conditioning compressor,( it needs a
motor to run it ) for an automobile, and use it in reverse, it pulls
a vacuum. Both will work, but again, results will vary depending on
the altitude (perhaps the attitude) you are at.

I believe what you are describing as a water powered vacuum pump is
usually called a filter pump or a Buchner pump, and used in nearly
all laboratories. They certainly work on the Venturi principle and
are surprisingly powerful; a vacuum of 3 centimetres of mercury is
easily obtained with a good fairly high pressure water supply. I used
to make them in glass and made 6 in 40 minutes for a technician’s
Certificate Any Scientific supplier will stock them in metal or
glass. But don’t operate one in areas and times of water shortage!